In the chemical and oil industry one of the most persistent problems relates to the cleaning of the various connecting pipes and tubes, for example, the tubes in cooling systems, heat-recovery exchangers and condensers. (The word "tube" or "tubes" will be used hereinafter, as appropriate.)
The process may be exemplified by the production of styrene monomer. Various types of polymers and copolymers are deposited in the heat-recovery exchangers and in the condensers. The fouling caused by the deposit of such polymers decreases the overall efficiency of the systems involved. It is, therefore, necessary to clean the systems internally. One method of cleaning which has been used involves the use of high pressure water. This method is inefficient and in many cases cannot remove completely the build-up of solids on the walls of the tubes. Thus with one conventional cleaning head long gouges are cut in the solids on the walls. Furthermore, the method is very time consuming and expensive. It is also dangerous to use because of the very high pressure water streams involved and is becoming more dangerous as the pressures used increase.
Another method involves drilling out the tube. Again, this method is very time consuming and expensive. Furthermore, the drill can often become embedded in the material to be drilled. Again, when very hard polymers are encountered, the drill bit may be deflected and drill through the tube wall. If this occurs, the tube has to be either removed or plugged in place thus decreasing the efficiency of the exchanger. Even if these problems are not encountered, drilling does not completely remove material deposited on the tube walls. Generally speaking any mechanical cutting, drilling, gouging etc. method tends to score the surface of the tube leaving a region in or on which deposits can build up. The tube is damaged and weakened and its useful life shortened.
Other methods include cleaning using chemical solvents. However, this method can only be used if there is a flow pathway remaining. In addition there is a trend away from chemical cleaning methods because of the disposal problem in relation to the used solvent.
Yet another method is to burn out a deposit. However, it may be necessary to remove a particular piece of apparatus from the site so that this procedure can be carried out.
Typically, it is necessary to use a combination of methods, such as a combination of the water blast and drilling methods. Even so, such a combination may succeed only in obtaining an increase in efficiency of the cleaned apparatus of up to 90%.
It is known in the art of extracting and distributing petroleum to pass a "pig" of solid material through a pipeline to wipe deposited paraffins from the wall. Furthermore, "pigging" is a known technique in the cleaning of tubes. However the pigs used are flexible and compressible and are often provided with abrasives embedded in their outer walls or with cutting or gouging devices projecting through their outer surface. Such a pig is forced through a tube by hydraulic action mechanically gouging material from the wall of the tube and pushing debris in front of it. The problem here is that the surface of the tube can also be scored, gouged and weakened.
Generally speaking, prior art methods of pigging have involved:
mechanical brushing, scraping or abrading by pigs specially designed for that purpose; and/or
low velocity passage through a tube, pushing the undesired material in front of the pig.
It is an object of the present invention to overcome the problems outlined above, that is, to provide a simple, relatively inexpensive, less dangerous and more efficient method of cleaning tubes.